Polarizing plate, optical film and image display

ABSTRACT

A polarizing plate of the present invention comprises a polarizer; an adhesive layer; and a transparent protective film bonded to at least one side of the polarizer with the adhesive layer interposed therebetween, wherein the adhesive layer is formed from an active energy ray curing adhesive containing at least one curable component, and the adhesive layer has a glass transition temperature (Tg) of 60° C. or more, and a thickness of 0.01 μm an to 5 μm. The polarizing plate has sufficient durability in a severe environment at high temperature and high humidity.

BACKGROUND OF THE PRESENT INVENTION

1. Field of the Present Invention

The present invention relates to a polarizing plate. The polarizingplate may be used alone or as a part of a laminated optical film to formliquid crystal displays (LCDs), organic EL displays, CRTs, PDPs, and soon.

2. Description of the Related Art

The liquid crystal display market has rapidly expanded in such fields asclocks, mobile phones, PDAs, note PCs, PC monitors, DVD players, andTVs. Liquid crystal displays use liquid crystal switching to visualizechanges in polarization state, and based on the display principle, theyuse polarizers. Particularly in TV applications and the like, there isan increasing demand for higher brightness, higher contrast, and widerviewing angle. Thus, higher transmittance, higher degree of polarizationand higher color reproducibility are also demanded of polarizing plates.

Iodine containing polarizer made of stretched polyvinyl alcohol in whichiodine is adsorbed has high transmittance and high degree ofpolarization and are most popular polarizers widely used. A generalpolarizing plate is produced by bonding a transparent protective film toboth sides of a polarizer with a so-called aqueous adhesive, which is asolution of a polyvinyl alcohol material in water (see Japanese PatentApplication Laid-Open (JP-A) Nos. 2006-220732 and 2001-296427).Triacetylcellulose or the like having high moisture permeability is usedfor the transparent protective film.

When an aqueous adhesive such as a polyvinyl alcohol adhesive is used inthe process of manufacturing the polarizing plate as described above,however, a drying process is necessary after the polarizer and thetransparent protective film are laminated. The presence of such a dryingprocess in manufacture of the polarizing plate is unfavorable in view ofan improvement in the productivity of the polarizing plate.

Also when an aqueous adhesive is used (in the case of so-called wetlamination), the polarizer must have a relatively high moisture contentsuch that the adhesion to the adhesive can be increased (in general, thepolarizer has a moisture content of about 30%). Otherwise, the aqueousadhesive cannot provide good adhesion in the resulting polarizing plate.However, the polarizing plate obtained as described above has a problemin which its dimensions can significantly change at high temperature orat high temperature and high humidity. On the other hand, in order tosuppress such a dimensional change, the moisture content of thepolarizer may be reduced, or a transparent protective film with lowmoisture permeability may be used. However, the lamination of such apolarizer and such a transparent protective film with an aqueousadhesive can lead to a reduction in the efficiency of the dryingprocess, a degradation in the polarizing properties, or defects ofappearance so that practically useful polarizing plates cannot beobtained.

In recent years, as the screen size of image displays (particularlytypified by TVs) increases, upsizing of polarizing plates becomes veryimportant in view of productivity and cost (an increase in yield and thenumber of available pieces). However, the polarizing plate using theaqueous adhesive has a problem in which a change in its size occurs bythe heat from a backlight to cause unevenness so that the so-calledlight leakage (unevenness) can be significant in which a black viewingdisplayed on the whole of the screen partially looks whitish.

Under the above-described circumstances, there are many proposals forthe use of active energy ray curing (particularly ultraviolet-raycuring) adhesives in place of aqueous adhesives. For example, anultraviolet-ray curing adhesive is proposed that includes an acrylicoligomer of epoxy acrylate, urethane acrylate, polyester acrylate, orthe like, and an acrylic or methacrylic monomer as a diluent (see JP-ANo. 61-246719).

In addition, durability performance required of polarizing platesbecomes strict, and durability under a more severe environment such as ahumid environment and a hot environment has been demanded. However, thepolarizing plate described above cannot have sufficient durability insuch a severe environment.

SUMMARY OF THE PRESENT INVENTION

It is an object of the present invention to provide a polarizing platethat has sufficient durability in a severe environment at hightemperature and high humidity.

It is another object of the present invention to provide an optical filmin which a polarizing plate is laminated and to provide an imagedisplay, such as a liquid crystal display, using such a polarizing plateor such an optical film.

As a result of investigations for solving the problems, the inventorshave found that the objects can be achieved with the polarizing platedescribed below, so that the present invention has been completed.

The present invention relates to a polarizing plate, comprising apolarizer; an adhesive layer; and a transparent protective film bondedto at least one side of the polarizer with the adhesive layer interposedtherebetween, wherein the adhesive layer is formed from an active energyray curing adhesive containing at least one curable component, and theadhesive layer has a glass transition temperature (Tg) of 60° C. ormore, and a thickness of 0.01 μm to 7 μm.

In the polarizing plate, the Tg (° C.) of the adhesive layer representedby A and the thickness (μm) of the adhesive layer represented by Bpreferably satisfy the mathematical formula (1): A−12×B>58.

In the polarizing plate, the adhesive layer preferably has a gelfraction of 50% by weight or more.

In the polarizing plate, the curable component is preferably a compoundhaving a (meth)acryloyl group.

In the polarizing plate, as the curable component, an N-substitutedamide monomer represented by the general formula (1):CH₂═C(R¹)—CONR²(R³), wherein R¹ represents a hydrogen atom or a methylgroup, R² represents a hydrogen atom or a straight or branched chainalkyl group having 1 to 4 carbon atoms and optionally having a hydroxylgroup, a mercapto group, an amino group, or a quaternary ammonium group,and R³ represents a hydrogen atom or a straight or branched chain alkylgroup having 1 to 4 carbon atoms, provided that R² and R³ are notsimultaneously a hydrogen atom, or R² and R³ are bonded to form afive-membered or six-membered ring optionally having an oxygen atom, ispreferably used.

As the N-substituted amide monomer, at least one selected fromN-hydroxyethylacrylamide, N-methylolacrylamide, N-isopropylacrylamide,and N-acryloylmorpholine, is preferable. Especially, the N-substitutedamide monomer preferably contains N-hydroxyethylacrylamide andN-acryloylmorpholine. When N-hydroxyethylacrylamide andN-acryloylmorpholine are both used, a content ofN-hydroxyethylacrylamide is preferably 40% by weight or more based onthe total amount of N-hydroxyethylacrylamide and N-acryloylmorpholine.

The curable component further may contain a monofunctional(meth)acrylate having an aromatic ring and a hydroxy group.

In the polarizing plate, the active energy ray curing adhesive ispreferably an electron beam curing adhesive.

In the polarizing plate, as a material of the transparent protectivefilm, at least one selected from a cellulose resin, a polycarbonateresin, a cyclic olefin polymer resin and a (meth)acrylic resin ispreferably used.

The present invention also relates to an optical film in which at leastone layer of the polarizing plate is laminated.

The present invention also relates to an image display, comprising thepolarizing plate or the optical film.

In the polarizing plate of the present invention, the active energy raycuring adhesive is used to bond the polarizer to the transparentprotective film. The active energy ray curing adhesive is more durablethan aqueous adhesives. Also in the polarizing plate of the presentinvention, the active energy ray curing adhesive is used such that theadhesive layer made from it can have a Tg of 60° C. or more, and thethickness of the adhesive layer is controlled to be from 0.01 to 7 μm.In the polarizing plate of the present invention, therefore, the activeenergy ray curing adhesive is used to form an adhesive layer with a highTg of 60° C. or more, and the thickness of the adhesive layer iscontrolled to be in the above range, so that the polarizing plate of thepresent invention can have sufficient durability under a severeenvironment at high humidity and high temperature. In particular, the Tg(° C.) of the adhesive layer (represented by A) and the thickness (μm)of the adhesive layer (represented by B) preferably satisfy themathematical formula (1): A−12×B>58, so that the durability can be at apreferred level.

The active energy ray curing adhesive for use in the polarizing plate ispreferably an electron beam curing adhesive. Electron beam curingadhesives can provide higher productivity than ultraviolet-ray curingadhesives. The use of an electron beam in the process of curing theadhesive used for bonding the polarizer to the transparent protectivefilm (specifically dry lamination) can eliminate a heating process,which would otherwise be necessary for an ultraviolet-ray curing method,and thus can provide very high productivity. Electron beam curingadhesives can further increase the durability of the polarizing plate ascompared with ultraviolet-ray curing adhesives.

When an (meth)acryloyl group-containing compound, specifically theN-substituted amide monomer, may be used as a curable component of theactive energy ray curing adhesive, such a curable component is preferredin terms of durability and particularly suitable for electron beamcuring adhesives. Electron beam curing adhesives can also exhibit goodadhesion to both a low-moisture-content polarizer and a transparentprotective film produced with a low-moisture-permeability material sothat the resulting polarizing plate can have a high level of dimensionalstability.

The use of the curable component described above allows the productionof polarizing plates whose dimensions are less changeable and thus canfacilitate upsizing of polarizing plates and keep the manufacturing costlow in terms of yield and the number of available pieces. The polarizingplate obtained in the present invention has a high level of dimensionalstability and thus can reduce unevenness caused by external heat from abacklight in an image display.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The polarizing plate of the present invention includes a polarizer, anadhesive layer and a transparent protective film provided on at leastone side of the polarizer with the adhesive layer interposedtherebetween. The adhesive layer is produced with an active energy raycuring adhesive. The active energy ray curing adhesive contains at leastone curable component.

The curable component used in the active energy ray curing adhesive isselected such that the adhesive layer made from the adhesive has a Tg of60° C. or more. In view of durability, the Tg of the adhesive layer ispreferably 70° C. or more, more preferably 75° C. or more, still morepreferably 100° C. or more, further more preferably 120° C. or more. Ifthe Tg of the adhesive layer is too high, the flexibility of thepolarizing plate can be low. Thus, the Tg of the adhesive layer ispreferably 300° C. or less, more preferably 240° C. or less, still morepreferably 180° C. or less.

The curable component may be a (meth)acryloyl group-containing compoundor a vinyl group-containing compound. Any of a monofunctional curablecomponent and a bifunctional or polyfunctional curable component may beused. One or more curable components may be selected and used singly orin combination so as to produce an adhesive layer with a Tg of 60° C. ormore. The curable component is preferably a (meth)acryloylgroup-containing compound. An N-substituted amide monomer is preferablyused as the (meth)acryloyl group-containing compound. Such a monomer ispreferred in view of adhesion. The term “(meth)acryloyl group” meansacryloyl group and/or methacryloyl group. As used herein, “meth” has thesame meaning as described above.

The N-substituted amide monomer may be represented by the generalformula (I): CH₂═C(R¹)—CONR²(R³), wherein R¹ represents a hydrogen atomor a methyl group, R² represents a hydrogen atom or a straight orbranched chain alkyl group having 1 to 4 carbon atoms and optionallyhaving a hydroxyl group, a mercapto group, an amino group, or aquaternary ammonium group, and R³ represents a hydrogen atom or astraight or branched chain alkyl group having 1 to 4 carbon atoms,provided that R² and R³ are not simultaneously a hydrogen atom, or R²and R³ are bonded to form a five-membered or six-membered ringoptionally having an oxygen atom. Concerning R² or R³ in the generalformula (I), the straight or branched chain alkyl group of 1 to 4 carbonatoms may be methyl, ethyl, isopropyl, or tert-butyl; the hydroxylgroup-containing alkyl group may be hydroxymethyl or hydroxyethyl; andthe amino group-containing alkyl group may be aminomethyl or aminoethyl.Alternatively, R² and R³ may be bonded to form an optionally oxygenatom-containing five- or six-membered ring, which may include anitrogen-containing heterocyclic ring. Examples of the heterocyclic ringinclude a morpholine ring, a piperidine ring, a pyrrolidine ring, and apiperazine ring.

Examples of the N-substituted amine monomer includeN-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide,N,N-diethyl(meth)acrylamide, N-isopropylacrylamide,N-butyl(meth)acrylamide, N-hexyl(meth)acrylamide,N-methylol(meth)acrylamide, N-hydroxyethyl(meth)acrylamide,N-methylol-N-propane(meth)acrylamide, aminomethyl(meth)acrylamide,aminoethyl(meth)acrylamide, mercaptomethyl(meth)acrylamide, andmercaptoethyl(meth)acrylamide. Examples of the heterocyclicring-containing monomer include N-acryloylmorpholine,N-acryloylpiperidine, N-methacryloylpiperidine, andN-acryloylpyrrolidine. One, or two or more of these N-substituted amidemonomers may be used singly or in combination.

The N-substituted amide monomer is preferably N-hydroxyethylacrylamide,N-methylolacrylamide, N-isopropylacrylamide, or N-acryloylmorpholine.N-substituted amide monomers exhibit good adhesion tolow-moisture-content polarizers or transparent protective films producedwith low moisture permeable materials. In particular, the monomerslisted above exhibit good adhesion, and N-hydroxyethylacrylamide isparticularly preferred.

One or two or more N-substituted amide monomers may be used singly or inany combination. When two or more N-substituted amide monomers are usedin combination, N-hydroxyethylacrylamide is preferably used incombination with N-acryloylmorpholine in view of durability andadhesion. In the case of this combination, the content ofN-hydroxyethylacrylamide is preferably 40% by weight or more based onthe total amount of N-hydroxyethylacrylamide and N-acryloylmorpholine,in terms of achieving good adhesion. The content ofN-hydroxyethylacrylamide is more preferably from 40 to 90% by weight,still more preferably from 60 to 90% by weight.

Besides the above, other (meth)acryloyl group-containing compounds foruse as the curable component include a variety of epoxy (meth)acrylates,urethane (meth)acrylates, and polyester (meth)acrylates, and a varietyof (meth)acrylate monomers. In particular, epoxy (meth)acrylates,specifically monofunctional (meth)acrylates having an aromatic ring anda hydroxy group are preferably used. If some of these curable componentsare incapable of forming an adhesive layer with a Tg of 60° C. or moreby themselves, they should be used in combination with the N-substitutedamide monomer.

A variety of monofunctional (meth)acrylates each having an aromatic ringand a hydroxy group may be used. The hydroxy group may be present as asubstituent on the aromatic ring, but in the present invention, it ispreferred that the hydroxy group is present on an organic group (bondedto a hydrocarbon group, specifically bonded to an alkylene group)linking the aromatic ring and (meth)acrylate.

The monofunctional (meth)acrylate having an aromatic ring and a hydroxygroup may be a reaction product of a monofunctional epoxy compoundhaving an aromatic ring with (meth)acrylic acid. Examples of themonofunctional epoxy compound having an aromatic ring include phenylglycidyl ether, tert-butyl phenyl glycidyl ether, and phenylpolyethylene glycol glycidyl ether. Examples of the monofunctional(meth)acrylate having an aromatic ring and a hydroxy group include2-hydroxy-3-phenoxypropyl (meth)acrylate,2-hydroxy-3-tert-butylphenoxypropyl (meth)acrylate, and2-hydroxy-3-phenyl polyethylene glycol propyl (meth)acrylate.

The (meth)acryloyl group-containing compound may also be a carboxylgroup-containing monomer, which is also preferred in view of adhesion.Examples of the carboxyl group-containing monomer include (meth)acrylicacid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate. Inparticular, acrylic acid is preferred.

Besides the above, other examples of the (meth)acryloyl group-containingcompound include alkyl (meth)acrylate having 1 to 12 carbon atoms suchas such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate,isononyl (meth)acrylate, and lauryl (meth)acrylate; alkoxyalkyl(meth)acrylate monomers such as methoxyethyl (meth)acrylate andethoxyethyl (meth)acrylate; hydroxyl group-containing monomers such as2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate,8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate,12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methylacrylate; acid anhydride group-containing monomers such as maleicanhydride and itaconic anhydride; caprolactone adducts of acrylic acid;sulfonate group-containing monomers such as styrenesulfonic acid,allylsulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid,(meth)acrylamidopropanesulfonic acid, sulfopropyl (meth)acrylate, and(meth)acryloyloxynaphthalenesulfonic acid; and phosphategroup-containing monomers such as 2-hydroxyethylacryloyl phosphate.Examples of other monomers also include (meth)acrylamide; maleimide,N-cyclohexylmaleimide, N-phenylmaleimide; alkylaminoalkyl (meth)acrylatemonomers such as aminoethyl (meth)acrylate, aminopropyl (meth)acrylate,N,N-dimethylaminoethyl (meth)acrylate, tert-butylaminoethyl(meth)acrylate, and 3-(3-pyrimidyl)propyl (meth)acrylate; andnitrogen-containing monomers including succinimide monomers such asN-(meth)acryloyloxymethylenesuccinimide,N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, andN-(meth)acryloyl-8-oxyoctamethylenesuccinimide.

As described above, the N-substituted amide monomer is preferably usedalone or in combination with the monofunctional (meth)acrylate having anaromatic ring and a hydroxy group to serve as the curable component ofthe active energy ray curing adhesive. When they are used incombination, the content of the N-substituted amide monomer ispreferably 40% by weight or more, more preferably 50% by weight or more,still more preferably 60% by weight or more, yet more preferably 70% byweight or more, further more preferably 80% by weight or more.

The curable component to be used may be a bifunctional or polyfunctionalcurable component. The bifunctional or polyfunctional curable componentis preferably bifunctional or polyfunctional (meth)acrylate,particularly preferably bifunctional or polyfunctional epoxy(meth)acrylate. Such bifunctional or polyfunctional epoxy (meth)acrylatemay be obtained by a reaction between a polyfunctional epoxy compoundand (meth)acrylic acid. Various polyfunctional epoxy compounds may belisted such as aromatic epoxy resins, alicyclic epoxy resins, andaliphatic epoxy resins.

Examples of aromatic epoxy resins include bisphenol epoxy resins such asbisphenol A diglycidyl ether, bisphenol F diglycidyl ether, andbisphenol S diglycidyl ether; novolac epoxy resins such as phenolnovolac epoxy resins, cresol novolac epoxy resins, andhydroxybenzaldehyde phenol novolac epoxy resins; and polyfunctionalepoxy resins such as glycidyl ether of tetrahydroxyphenylmethane,glycidyl ether of tetrahydroxybenzophenone, and epoxidized polyvinylphenol.

Examples of alicyclic epoxy resins include hydrogenated products of theabove aromatic epoxy resins, cyclohexane type epoxy resins, cyclohexylmethyl ester type epoxy resins, cyclohexyl methyl ether type epoxyresins, spiro type epoxy resins, and tricyclodecane type epoxy resins.

Examples of aliphatic epoxy resins include polyglycidyl ethers ofaliphatic polyhydric alcohols or alkylene oxide adducts thereof.Examples thereof include diglycidyl ether of 1,4-butanediol, diglycidylether of 1,6-hexanediol, glycerol triglycidyl ether, triglycidyl etherof trimethylolpropane, diglycidyl ether of polyethylene glycol,diglycidyl ether of propylene glycol, and polyglycidyl ethers ofpolyether polyol produced by adding one or two or more alkylene oxides(such as ethylene oxide and propylene oxide) to an aliphatic polyhydricalcohol such as ethylene glycol, propylene glycol, and glycerin.

The epoxy resin generally has an epoxy equivalent of 30 to 3000g/equivalent, preferably of 50 to 1500 g/equivalent.

The bifunctional or polyfunctional epoxy (meth)acrylate is preferablyepoxy (meth)acrylate of an aliphatic epoxy resin, particularlypreferably epoxy (meth)acrylate of a bifunctional aliphatic epoxy resin.

In addition to the curable component, the active energy ray curingadhesive according to the present invention may further contain anappropriate additive, if necessary. The active energy ray curingadhesive to be used may be an electron beam curing-type orultraviolet-ray curing adhesive. When the adhesive to be used is of anelectron beam curing-type, it is not always necessary to add aphotopolymerization initiator to the adhesive. On the other hand, whenthe adhesive to be used is of an ultraviolet-ray curing-type, aphotopolymerization initiator is used. The photopolymerization initiatoris generally used in an amount of about 0.1 to about 10 parts by weight,preferably of 0.5 to 3 parts by weight, based on 100 parts by weight ofthe curable component.

Examples of the additive include sensitizers for increasing the electronbeam-curing rate or sensitivity, such as carbonyl compounds, adhesionpromoters such as silane coupling agents and ethylene oxide, additivesfor improving wettability with the transparent protective film,additives for improving mechanical strength or workability, such asacryloxy group-containing compounds or hydrocarbons (natural orsynthetic resins), ultraviolet-absorbing agents, age resistors, dyes,processing aids, ion-trapping agents, antioxidants, tackifiers, fillers(other than metal compound fillers), plasticizers, leveling agents,antifoaming agents, and antistatic agents.

The polarizer may be made of a polyvinyl alcohol resin. The polarizer tobe used may be produced by dyeing a polyvinyl alcohol resin film with adichroic material (typically iodine or a dichroic dye) and uniaxiallystretching the film. The polyvinyl alcohol resin constituting thepolyvinyl alcohol resin film preferably has a degree of polymerizationof 100 to 5000, more preferably of 1400 to 4000. If its polymerizationdegree is too low, it can tend to be broken in the process of stretchingat a certain ratio. If its degree of polymerization is too high, unusualtension can be required for the stretching process, and thus mechanicalstretching of it can be impossible.

The polyvinyl alcohol resin film for forming the polarizer may be formedby any appropriate method (such as an extrusion method, a casting methodor a flow casting method of casting a solution obtained by dissolving aresin in water or an organic solvent to form a film). The thickness ofthe polarizer is generally about 5 to about 80 μm, while it may bedetermined as necessary depending on the purpose or application of theLCD for which the polarizing plate is used.

Any appropriate method may be used to produce the polarizer, dependingon the purpose, the materials to be used, and the conditions. Forexample, a method that may be used includes subjecting the polyvinylalcohol resin film to a series of manufacturing steps generallyincluding swelling, dyeing, crosslinking, stretching, washing withwater, and drying. Except for the drying step, each step may beperformed while the polyvinyl alcohol resin film is immersed in a bathcontaining a solution necessary for each step. Concerning the steps ofswelling, dyeing, crosslinking, stretching, washing with water, anddrying, the order of the steps, the number of times of each step, or thepresence or absence of each step may be appropriately determineddepending on the purpose, the materials to be used and the conditions.For example, some steps may be simultaneously performed in a singleprocess, and swelling, dyeing and crosslinking may be performed at thesame time. For example, crosslinking before or after stretching ispreferably employed. For example, washing with water may be performedafter all of the other steps or only after a certain step.

The swelling step is typically performed by immersing the polyvinylalcohol resin film in a treatment bath containing water. By thistreatment, the surface of the polyvinyl alcohol resin film is cleaned ofdirt and an anti-blocking agent, and the polyvinyl alcohol resin film isallowed to swell so that unevenness such as uneven dyeing can beprevented. Glycerin, potassium iodide and so on may be added, asappropriate, to the swelling bath. The temperature of the swelling bathis generally from about 20 to about 60° C., and the time of immersion inthe swelling bath is generally from about 0.1 to about 10 minutes.

The dyeing step is typically performed by immersing the polyvinylalcohol resin film in a treatment bath containing a dichroic materialsuch as iodine. Water is generally used as a solvent for the dyeing bathsolution, to which a proper amount of an organic solvent compatible withwater may be added. The dichroic material is generally used in an amountof 0.1 to 1 part by weight, based on 100 parts by weight of the solvent.When iodine is used as the dichroic material, the dyeing bath solutionpreferably contain an aid such as an iodide, so that the dyeingefficiency can be improved. The aid is preferably used in an amount of0.02 to 20 parts by weight, more preferably of 2 to 10 parts by weight,based on 100 parts by weight of the solvent. Examples of the iodideinclude potassium iodide, lithium iodide, sodium iodide, zinc iodide,aluminum iodide, lead iodide, copper iodide, barium iodide, calciumiodide, tin iodide, and titanium iodide. The temperature of the dyeingbath is generally from about 20 to about 70° C., and the time ofimmersion in the dyeing bath is generally from about 1 to about 20minutes.

The crosslinking step is typically performed by immersing the dyedpolyvinyl alcohol resin film in a treatment bath containing acrosslinking agent. Any appropriate crosslinking agent may be used.Examples of the crosslinking agent include boron compounds such as boricacid and borax, glyoxal, and glutaraldehyde. One or more of thesecrosslinking agents may be used alone or in combination. Water isgenerally used as a solvent for the crosslinking bath solution, to whicha proper amount of an organic solvent compatible with water may beadded. The crosslinking agent is generally used in an amount of 1 to 10parts by weight, based on 100 parts by weight of the solvent. If thecontent of the crosslinking agent is less than 1 part by weight, theresulting optical properties can be insufficient. If the content of thecrosslinking agent is more than 10 parts by weight, large stress can beapplied to the film during stretching so that the resulting polarizingplate could be shrunk. The crosslinking bath solution preferablycontains an aid such as an iodide, so that uniform in-plane propertiescan be easily obtained. The concentration of the aid is preferably from0.05 to 15% by weight, more preferably from 0.5 to 8% by weight.Examples of the iodide may be the same as in the case of the dyeingstep. The temperature of the crosslinking bath is generally from about20 to about 70° C., preferably from 40 to 60° C. The time of immersionin the crosslinking bath is generally from about 1 second to about 15minutes, preferably from 5 seconds to 10 minutes.

As described above, the stretching step may be performed at any stage.Specifically, the stretching step may be performed before or after thedyeing step, may be performed simultaneously with the swelling step, thedyeing step, and the crosslinking step, or may be performed after thecrosslinking step. The polyvinyl alcohol resin film is generallystretched to a total stretch ratio of 5 times or more, preferably of 5to 7 times, more preferably of 5 to 6.5 times. If the total stretchratio is less than 5 times, it can be difficult to produce a polarizingplate with a high degree of polarization. If the total stretch ratio ismore than 7 times, the polyvinyl alcohol resin film can tend to bebroken. Any appropriate specific stretching method may be used. Forexample, when a wet stretching method is used, the polyvinyl alcoholresin film may be stretched to a specific stretch ratio in a treatmentbath. The stretching bath solution to be used is preferably produced byadding various metal salts, iodine, boric acid, or a zinc compound to asolvent such as water or an organic solvent such as ethanol.

The step of washing with water is typically performed by immersing thepolyvinyl alcohol resin film on which the above-described varioustreatments are carried out in a treatment bath. Unnecessary residues canbe washed away from the polyvinyl alcohol resin film by the step ofwashing with water. The water-washing bath may be of pure water or anaqueous solution of an iodide such as potassium iodide and sodiumiodide. The aqueous iodide solution preferably has a concentration of0.1 to 10% by weight. An aid such as zinc sulfate and zinc chloride maybe added to the aqueous iodide solution. The temperature of thewater-washing bath is preferably from 10 to 60° C., more preferably from30 to 40° C. The immersion time may be from 1 second to 1 minute. Thestep of washing with water may be performed only once or twice or more,if necessary. When the step of washing with water is performed twice ormore, the type and concentration of the additive contained in thewater-washing bath for each treatment may be controlled as appropriate.For example, the step of washing with water may include immersing thepolyvinyl alcohol resin film in an aqueous potassium iodide solution(0.1 to 10% by weight, 10 to 60° C.) for 1 second to 1 minute after anyof the above treatments and rinsing the film with pure water. In thestep of washing with water, an organic solvent compatible with water(such as ethanol) may be added as appropriate in order to modify thesurface of the polarizer or increase the efficiency of drying of thepolarizer.

Any appropriate methods such as natural drying, blow drying, and dryingby heating may be used in the drying step. In the case of drying byheating, for example, the drying temperature is generally from about 20to about 80° C., and the drying time is generally from about 1 to about10 minutes. The polarizer may be obtained as described above.

The polarizer for use in the present invention preferably has a moisturecontent of 20% by weight or less, more preferably of 0 to 15% by weight,still more preferably of 1 to 15% by weight. If the moisture content ismore than 20% by weight, the size of the resulting polarizing plate cansignificantly change, and there is a possibility of causing a problem isin which the change in size can be significant at high temperature or athigh temperature and high humidity.

The moisture content of the polarizer for use in the present inventionmay be adjusted by any appropriate method. For example, the moisturecontent may be adjusted by controlling the conditions of the drying stepin the process of manufacturing the polarizer.

The moisture content of the polarizer may be measured by the methoddescribed below. A sample (100×100 mm in size) is cut from thepolarizer, and the initial weight of the sample is measured. The sampleis then dried at 120° C. for 2 hours and measured for dry weight. Themoisture content is determined according to the following formula:moisture content (% by weight)={(the initial weight)−(the dryweight)/(the initial weight)}×100. The measurement of each weight isperformed three times, and the average value is used.

A thermoplastic resin with a high level of transparency, mechanicalstrength, thermal stability, moisture blocking properties, isotropy, andthe like may be used as a material for forming the transparentprotective film. Examples of such a thermoplastic resin includecellulose resins such as triacetylcellulose, polyester resins,polyethersulfone resins, polysulfone resins, polycarbonate resins,polyamide resins, polyimide resins, polyolefin resins, (meth)acrylicresins, cyclic olefin polymer resins (norbornene resins), polyarylateresins, polystyrene resins, polyvinyl alcohol resins, and any mixturethereof. The transparent protective film is generally laminated to oneside of the polarizer with the adhesive layer, but thermosetting resinsor ultraviolet curing resins such as (meth)acrylic, urethane, acrylicurethane, epoxy, or silicone resins may be used to other side of thepolarizer for the transparent protective film. The transparentprotective film may also contain at least one type of any appropriateadditive. Examples of the additive include an ultraviolet absorbingagent, an antioxidant, a lubricant, a plasticizer, a release agent, ananti-discoloration agent, a flame retardant, a nucleating agent, anantistatic agent, a pigment, and a colorant. The content of thethermoplastic resin in the transparent protective film is preferablyfrom 50 to 100% by weight, more preferably from 50 to 99% by weight,still more preferably from 60 to 98% by weight, particularly preferablyfrom 70 to 97% by weight. If the content of the thermoplastic resin inthe transparent protective film is 50% by weight or less, hightransparency and other properties inherent in the thermoplastic resincan fail to be sufficiently exhibited.

Moreover, as is described in JP-A No. 2001-343529 (WO 01/37007), polymerfilms, for example, resin compositions including (A) thermoplasticresins having substituted and/or non-substituted imido group insidechain, and (B) thermoplastic resins having substituted and/ornon-substituted phenyl and nitrile group in sidechain may be mentioned.As an illustrative example, a film may be mentioned that is made of aresin composition including alternating copolymer comprisingiso-butylene and N-methyl maleimide, and acrylonitrile-styrenecopolymer. A film comprising mixture extruded article of resincompositions etc. may be used. Since the films are less in retardationand less in photoelastic coefficient, faults such as unevenness due to astrain in a polarizing plate can be removed and besides, since they areless in moisture permeability, they are excellent in durability underhumidified environment.

Thickness of the transparent protective film can be properly determinedand generally in the range of from about 1 to about 500 μm from theviewpoint of a strength, workability such as handlability, requirementfor a thin film and the like. Especially, the thickness is preferably inthe range of from 1 to 300 μm and more preferably in the range of from 5to 200 μm. Therefore, it is particularly preferred that the transparentprotective film has a thickness of 5 to 150 μm.

Note that in a case where the transparent protective films are providedon both sides of a polarizer, the protective films made from the samepolymer may be used on both sides thereof or alternatively, theprotective films made from polymer materials different from each othermay also be used on respective both sides thereof.

At least one selected from a cellulose resin, a polycarbonate resin, acyclic polyolefin resin, and a (meth)acrylic resin is preferably usedfor the transparent protective film according to the present invention.The electron beam curing adhesive for use in the polarizing plateaccording to the present invention exhibits good adhesion to varioustypes of transparent protective films. In particular, the electron beamcuring adhesive for use in the polarizing plate according to the presentinvention exhibits good adhesion to acrylic resins, to which it has beendifficult to provide satisfactory adhesion by conventional techniques.

The cellulose resin is an ester of cellulose and a fatty acid. Examplesof such a cellulose ester resin include triacetyl cellulose, diacetylcellulose, tripropionyl cellulose, dipropionyl cellulose, and the like.In particular, triacetyl cellulose is preferred. Much commerciallyavailable triacetyl celluloses are placing on sale and are advantageousin view of easy availability and cost. Examples of commerciallyavailable products of triacetyl cellulose include UV-50, UV-80, SH-80,TD-80U, TD-TAC, and UZ-TAC (trade names) manufactured by FujifilmCorporation, and KC series manufactured by Konica Minolta. In general,these triacetyl cellulose products have a thickness directionretardation (Rth) of about 60 nm or less, while having an in-planeretardation (Re) of almost zero.

Cellulose resin films with relatively small thickness directionretardation may be obtained by processing any of the above celluloseresins. Examples of the processing method include a method that includeslaminating a general cellulose-based film to a base film such as apolyethylene terephthalate, polypropylene, or stainless steel film,coated with a solvent such as cyclopentanone or methyl ethyl ketone,drying the laminate by heating (for example, at 80 to 150° C. for 3 to10 minutes) and then separating the base film; and a method thatincludes coating a general cellulose resin film with a solution of anorbornene resin, a (meth)acrylic resin or the like in a solvent such ascyclopentanone or methyl ethyl ketone, drying the coated film by heating(for example, at 80 to 150° C. for 3 to 10 minutes), and then separatingthe coating.

The cellulose resin film with a relatively small thickness directionretardation to be used may be a fatty acid cellulose resin film with acontrolled degree of fat substitution. While triacetyl cellulose forgeneral use has a degree of acetic acid substitution of about 2.8,preferably, the degree of acetic acid substitution is controlled to 1.8to 2.7, so that the Rth can be reduced. The Rth may also be controlledto be low by adding a plasticizer such as dibutyl phthalate,p-toluenesulfonanilide, and acetyl triethyl citrate, to the fattyacid-substituted cellulose resin. The plasticizer is preferably added inamount of 40 parts by weight or less, more preferably of 1 to 20 partsby weight, still more preferably of 1 to 15 parts by weight, to 100parts by weight of the fatty acid cellulose resin.

For example, the cyclic polyolefin resin is preferably a norborneneresin. Cyclic olefin resin is a generic name for resins produced bypolymerization of cyclic olefin used as a polymerizable unit, andexamples thereof include the resins disclosed in JP-A Nos. 01-240517,03-14882, and 03-122137. Specific examples thereof include ring-opened(co)polymers of cyclic olefins, addition polymers of cyclic olefins,copolymers (typically random copolymers) of cyclic olefins and α-olefinssuch as ethylene and propylene, graft polymers produced by modificationthereof with unsaturated carboxylic acids or derivatives thereof, andhydrides thereof. Examples of the cyclic olefin include norbornenemonomers.

Various commercially available cyclic polyolefin resins are placing onsale. Examples thereof include Zeonex (trade name) and Zeonor (tradename) series manufactured by Zeon Corporation, Arton (trade name) seriesmanufactured by JSR Corporation, Topas (trade name) series manufacturedby Ticona, and Apel (trade name) series manufactured by MitsuiChemicals, Inc.

The (meth)acrylic resin preferably has a glass transition temperature(Tg) of 115° C. or more, more preferably of 120° C. or more, still morepreferably of 125° C. or more, particularly preferably of 130° C. ormore. If the Tg is 115° C. or more, the resulting polarizing plate canhave good durability. The upper limit to the Tg of the (meth)acrylicresin is preferably, but not limited to, 170° C. or less, in view offormability and the like. The (meth)acrylic resin can form a film withan in-plane retardation (Re) of almost zero and a thickness directionretardation (Rth) of almost zero.

Any appropriate (meth)acrylic resin may be used as long as theadvantages of the present invention are not reduced. Examples of such a(meth)acrylic resin include poly(meth)acrylate such as poly(methylmethacrylate), methyl methacrylate-(meth)acrylic acid copolymers, methylmethacrylate-(meth)acrylate copolymers, methylmethacrylate-acrylate-(meth)acrylic acid copolymers, methyl(meth)acrylate-styrene copolymers (such as MS resins), and alicyclichydrocarbon group-containing polymers (such as methylmethacrylate-cyclohexyl methacrylate copolymers and methylmethacrylate-norbornyl (meth)acrylate copolymers). Poly(C₁₋₆ alkyl(meth)acrylate) such as poly(methyl (meth)acrylate) is preferred, and amethyl methacrylate-based resin mainly composed of a methyl methacrylateunit (50 to 100% by weight, preferably 70 to 100% by weight) is morepreferred.

Examples of the (meth)acrylic resin include Acrypet VH and AcrypetVRL20A each manufactured by Mitsubishi Rayon Co., Ltd., (meth)acrylicresins having a ring structure in their molecule as disclosed in JP-ANo. 2004-70296, and high-Tg (meth)acrylic resins produced byintramolecular crosslinking or intramolecular cyclization reaction.

Lactone ring structure-containing (meth)acrylic resins may also be used,because they have high heat resistance and high transparency and alsohave high mechanical strength after biaxially stretched.

Examples of the lactone ring structure-containing (meth)acrylic reinsinclude the lactone ring structure-containing (meth)acrylic reinsdisclosed in JP-A Nos. 2000-230016, 2001-151814, 2002-120326,2002-254544, and 2005-146084.

The lactone ring structure-containing (meth)acrylic reins preferablyhave a ring structure represented by Formula (I):

wherein R¹, R² and R³ each independently represent a hydrogen atom or anorganic residue of 1 to 20 carbon atoms. The organic residue may containan oxygen atom(s).

The content of the lactone ring structure represented by Formula (I) inthe lactone ring structure-containing (meth)acrylic resin is preferablyfrom 5 to 90% by weight, more preferably from 10 to 70% by weight, stillmore preferably from 10 to 60% by weight, particularly preferably from10 to 50% by weight. If the content of the lactone ring structurerepresented by Formula (I) in the lactone ring structure-containing(meth)acrylic resin is less than 5% by weight, its heat resistance,solvent resistance or surface hardness can be insufficient. If thecontent of the lactone ring structure represented by Formula (I) in thelactone ring structure-containing (meth)acrylic resin is more than 90%by weight, its formability or workability can be poor.

The lactone ring structure-containing (meth)acrylic resin preferably hasa mass average molecular weight (also referred to as weight averagemolecular weight) of 1,000 to 2,000,000, more preferably of 5,000 to1,000,000, still more preferably of 10,000 to 500,000, particularlypreferably of 50,000 to 500,000. A mass average molecular weight outsidethe above range is not preferred in view of formability or workability.

The lactone ring structure-containing (meth)acrylic resin preferably hasa Tg of 115° C. or more, more preferably of 120° C. or more, still morepreferably of 125° C. or more, particularly preferably of 130° C. ormore. For example, the resin with a Tg of 115° C. or more can producegood durability, when it is incorporated in the form of a transparentprotective film in a polarizing plate. The upper limit to the Tg of thelactone ring structure-containing (meth)acrylic resin is preferably, butnot limited to, 170° C. or less in view of formability and the like.

The total light transmittance of the lactone ring structure-containing(meth)acrylic resin, which may be measured according to ASTM-D-1003 withrespect to injection molded products, is preferably as high as possible,and specifically, it is preferably 85% or more, more preferably 88% ormore, still more preferably 90% or more. The total light transmittanceis an index of transparency, and a total light transmittance of lessthan 85% can result in reduced transparency.

The transparent protective film to be used generally has an in-planeretardation of less than 40 nm and a thickness direction retardation ofless than 80 nm. The in-plane retardation Re is expressed by the formulaRe=(nx−ny)×d, the {circumflex over (t)}hickness direction retardationRth is expressed by the formula Rth=(nx−nz)×d, and the Nz coefficient isrepresented by the formula Nz=(nx−nz)/(nx−ny), where nx, ny and nz arethe refractive indices of the film in the directions of its slow axis,fast axis and thickness, respectively, d is the thickness (nm) of thefilm, and the direction of the slow axis is a direction in which thein-plane refractive index of the film is maximum. Moreover, it ispreferable that the transparent protective film may have as littlecoloring as possible. A protective film having a thickness directionretardation of from −90 nm to +75 nm may be preferably used. Thus,coloring (optical coloring) of polarizing plate resulting from aprotective film may mostly be cancelled using a protective film having athickness direction retardation (Rth) of from −90 nm to +75 nm. Thethickness direction retardation (Rth) is preferably from −80 nm to +60nm, and especially preferably from −70 nm to +45 nm.

Alternatively, the transparent protective film to be used may be aretardation plate having an in-plane retardation of 40 nm or more and/ora thickness direction retardation of 80 nm or more. The in-planeretardation is generally controlled in the range of 40 to 200 nm, andthe thickness direction retardation is generally controlled in the rangeof 80 to 300 nm. The retardation plate for use as the transparentprotective film also has the function of the transparent protective filmand thus can contribute to a reduction in thickness.

Examples of the retardation plate include a birefringent film producedby uniaxially or biaxially stretching a polymer material, an orientedliquid crystal polymer film, and an oriented liquid crystal polymerlayer supported on a film. The thickness of the retardation plate isgenerally, but not limited to, from about 20 to about 150 μm.

Examples of the polymer material include polyvinyl alcohol, polyvinylbutyral, poly(methyl vinyl ether), poly(hydroxyethyl acrylate),hydroxyethyl cellulose, hydroxypropyl cellulose, methylcellulose,polycarbonate, polyarylate, polysulfone, polyethylene terephthalate,polyethylene naphthalate, polyethersulfone, polyphenylene sulfide,polyphenylene oxide, polyallylsulfone, polyamide, polyimide, polyolefin,polyvinyl chloride, cellulose resins, cyclic polyolefin resins(norbornene reins), and various types of binary or ternary copolymersthereof, graft copolymers thereof, and any blend thereof. Any of thesepolymer materials may be formed into an oriented product (a stretchedfilm) by stretching or the like.

Examples of the liquid crystal polymer include various main-chain orside-chain types having a liquid crystal molecular orientationproperty-imparting conjugated linear atomic group (mesogen) introducedin a main or side chain of a polymer. Examples of the main chain typeliquid crystal polymer include polymers having a mesogen group bondedthereto via a flexibility-imparting spacer moiety, such as nematicallyordered polyester liquid-crystalline polymers, discotic polymers, andcholesteric polymers. For example, the side-chain type liquid crystalpolymer may be a polymer comprising: a main chain skeleton ofpolysiloxane, polyacrylate, polymethacrylate, or polymalonate; and aside chain having a mesogen moiety that comprises a nematicorientation-imparting para-substituted cyclic compound unit and isbonded thereto via a spacer moiety comprising a conjugated atomic group.For example, any of these liquid crystal polymers may be applied by aprocess that includes spreading a solution of the liquid crystallinepolymer on an alignment surface such as a rubbed surface of a thin filmof polyimide, polyvinyl alcohol or the like, formed on the glass plate,and an obliquely vapor-deposited silicon oxide surface, andheat-treating it.

The retardation plate may have any appropriate retardation depending onthe intended use such as compensation for coloration, viewing angle, orthe like due to the birefringence of various wave plates or liquidcrystal layers. Two or more types of retardation plates may also belaminated to provide controlled optical properties, includingretardation.

A retardation plate satisfying the relation: nx=ny>nz, nx>ny>nz,nx>ny=nz, nx>nz>ny, nz-nx>ny, nz>nx>ny, or nz>nx=ny may be selected andused depending on various applications. The relation ny-nz includes notonly the case where ny is completely equal to nz but also the case whereny is substantially equal to nz.

For example, the retardation plate satisfying the relation nx>ny>nz tobe used preferably has a in-plane retardation of 40 to 100 nm, athickness retardation of 100 to 320 nm, and an Nz coefficient of 1.8 to4.5. For example, the retardation plate satisfying the relation nx>ny=nz(positive A plate) to be used preferably has a in-plane retardation of100 to 200 nm. For example, the retardation plate satisfying therelation nz=nx>ny (negative A plate) to be used preferably has ain-plane retardation of 100 to 200 nm. For example, the retardationplate satisfying the relation nx>nz>ny to be used preferably has ain-plane retardation of 150 to 300 nm and an Nz coefficient of more than0 and not more than 0.7. As described above, for example, theretardation plate satisfying the relation nx=ny>nz, nz>nx>ny or nz>nx=nymay also be used.

The transparent protective film may be appropriately selected dependingon the liquid crystal display to be produced therewith. In the case ofVA (Vertical Alignment, including MVA and PVA), it is preferred that thetransparent protective film on at least one side of the polarizing plate(on the cell side) has a retardation. Specifically, it preferably has aretardation Re in the range of 0 to 240 nm and a retardation Rth in therange of 0 to 500 nm. In terms of three-dimensional refractive index,the case of nx>ny=nz, nx>ny>nz, nx>nz>ny, or nx=ny>nz (uniaxial,biaxial, Z conversion, negative C-plate) is preferred. When polarizingplates are used on upper and lower sides of a liquid crystal cell, thetransparent protective films may have a retardation on upper and lowersides of the liquid crystal cell, or one of the upper and lowertransparent protective films may has a retardation.

For example, in the case of IPS (In-Plane Switching, including FFS), thetransparent protective film for use in one of the polarizing plates mayhave or may not have a retardation. For example, a transparentprotective film with no retardation is preferably provided on both upperand lower sides of a liquid crystal cell (cell sides), or otherwise atransparent protective film with a retardation is preferably provided onboth or one of the upper and lower sides of a liquid crystal cell (forexample, Z conversion on the upper side with no retardation on the lowerside or an A-plate provided on the upper side with a positive C-plateprovided on the lower side). When it has a retardation, it preferablyhas a retardation Re in the range of −500 to 500 nm and a retardationRth in the range of −500 to 500 nm. In terms of three-dimensionalrefractive index, nx>ny=nz, nx>nz>ny, nz>nx=ny, or nz>nx>ny (uniaxial, Zconversion, positive C-plate, positive A-plate) is preferred.

The film with retardation may be separately prepared and laminated to atransparent protective film with no retardation so that the functiondescribed above can be provided.

The polarizer or the transparent protective film may be subjected tosurface modification treatment before it is applied with the adhesive.Specific examples of such treatment include corona treatment, plasmatreatment, primer treatment, saponification treatment, and couplingagent treatment.

A hard coat layer may be prepared, or antireflection processing,processing aiming at sticking prevention, diffusion or anti glare may beperformed onto the face on which the polarizing film of the abovedescribed transparent protective film has not been adhered.

A hard coat processing is applied for the purpose of protecting thesurface of the polarizing plate from damage, and this hard coat film maybe formed by a method in which, for example, a curable coated film withexcellent hardness, slide property etc. is added on the surface of theprotective film using suitable ultraviolet curable type resins, such asacrylic type and silicone type resins. Antireflection processing isapplied for the purpose of antireflection of outdoor daylight on thesurface of a polarizing plate and it may be prepared by forming anantireflection film according to the conventional method etc. Besides, asticking prevention processing is applied for the purpose of adherenceprevention with adjoining layer.

In addition, an anti glare processing is applied in order to prevent adisadvantage that outdoor daylight reflects on the surface of apolarizing plate to disturb visual recognition of transmitting lightthrough the polarizing plate, and the processing may be applied, forexample, by giving a fine concavo-convex structure to a surface of theprotective film using, for example, a suitable method, such as roughsurfacing treatment method by sandblasting or embossing and a method ofcombining transparent fine particle. As a fine particle combined inorder to form a fine concavo-convex structure on the above-mentionedsurface, transparent fine particles whose average particle size is 0.5to 50 μm, for example, such as inorganic type fine particles that mayhave conductivity comprising silica, alumina, titania, zirconia, tinoxides, indium oxides, cadmium oxides, antimony oxides, etc., andorganic type fine particles comprising cross-linked of non-cross-linkedpolymers may be used. When forming fine concavo-convex structure on thesurface, the amount of fine particle used is usually about 2 to 70weight parts to the transparent resin 100 weight parts that forms thefine concavo-convex structure on the surface, and preferably 5 to 50weight parts. An anti glare layer may serve as a diffusion layer(viewing angle expanding function etc.) for diffusing transmitting lightthrough the polarizing plate and expanding a viewing angle etc.

In addition, the above-mentioned antireflection layer, stickingprevention layer, diffusion layer, anti glare layer, etc. may be builtin the protective film itself, and also they may be prepared as anoptical layer different from the protective film.

The polarizing plate according to the present invention may be producedby bonding the transparent protective film to the polarizer with theadhesive described above. This production method may include the stepsof: applying the adhesive to the surface of the polarizer for receivingthe adhesive layer and/or to the surface of the transparent protectivefilm for receiving the adhesive layer; laminating the polarizer and thetransparent protective film with the polarizing plate adhesiveinterposed therebetween; and irradiating an active energy ray (such asan electron beam or an ultraviolet ray) to the laminate of the polarizerand the transparent protective film bonded with the polarizing plateadhesive interposed therebetween to form an adhesive layer.

Any appropriate coating method for applying the adhesive may be chosendepending on the viscosity of the adhesive or the desired thickness.Examples of coating methods include reverse coating, gravure coating(direct, reverse or offset), bar reverse coating, roll coating, diecoating, bar coating, and rod coating. A dipping method or any othercoating method may also be suitably used for coating.

The polarizer is laminated to the transparent protective film with theadhesive coating interposed therebetween. The lamination of thepolarizer and the transparent protective film may be performed using aroll laminator or the like.

After the polarizer and the transparent protective film are laminated,the adhesive is cured by the irradiation of an active energy ray (suchas an electron beam or an ultraviolet ray). The active energy ray (suchas an electron beam or an ultraviolet ray) may be applied in anyappropriate direction. The active energy ray is preferably applied fromthe transparent protective film side. There is a possibility that theapplication of the active energy ray (such as an electron beam or anultraviolet ray) from the polarizer side could lead to degradation ofthe polarizer.

The active energy ray curing adhesive to be used is preferably anelectron beam curing adhesive. Any appropriate conditions under whichthe adhesive can be cured may be used for the irradiation of an electronbeam. For example, an electron beam is preferably irradiated at anaccelerating voltage of 5 kV to 300 kV, more preferably of 10 kV to 250kV. If the accelerating voltage is less than 5 kV, the electron beam canfail to reach the adhesive so that the curing can be insufficient. Ifthe accelerating voltage is more than 300 kV, the degree of penetrationthrough the object can be too high so that the electron beam can bereflected to damage the transparent protective film or the polarizer.The irradiation dose is preferably from 5 to 100 kGy, more preferablyfrom 10 to 75 kGy. If the irradiation dose is less than 5 kGy, theadhesive can be insufficiently cured. An irradiation dose of more than100 kGy can damage the transparent protective film or the polarizer andcause a reduction in mechanical strength or yellow discoloration so thatthe desired optical properties cannot be achieved.

When an ultraviolet ray is irradiated for curing, a polymerizationinitiator may be added in an amount of 0.1 to 5 parts by weight based on100 parts by weight of the curable component, preferably of 1 to 4 partsby weight, more preferably of 2 to 3 parts by weight. Any appropriateconditions under which the adhesive can be cured may be employed for theirradiation of an ultraviolet ray. The ultraviolet irradiation dose ispreferably from 100 to 500 mJ, more preferably from 200 to 400 mJ.

In the polarizing plate obtained as described above according to thepresent invention, the adhesive layer has a thickness of 0.01 to 7 μm,preferably of 0.01 to 5 μm, more preferably of 0.01 to 2 μm, still morepreferably of 0.01 to 1 μm. If the thickness is less than 0.01 μm, theadhesive can fail to produce a cohesive force by itself so that there isa possibility that adhesive strength fails to be established. If thethickness of the adhesive layer is more than 7 μm, the polarizing platemay fail to have sufficient durability.

The adhesive layer preferably has a gel fraction of 50% by weight ormore in terms of having sufficient durability. The gel fraction is morepreferably 60% by weight or more, still more preferably 70% by weight ormore. The gel fraction may be measured by the method described inExamples.

The electron beam irradiation is generally performed in an inert gas. Ifnecessary, a small amount of air or oxygen may be introduced under theconditions for the irradiation. Oxygen may be introduced as appropriatedepending on the material of the transparent protective film. In such acase, the electron beam initially irradiated to the surface of thetransparent protective film is intentionally inhibited by the oxygen sothat the transparent protective film can be prevented from being damagedand that the electron beam can be efficiently irradiated only to theadhesive.

When the production method is performed on a continuous line, the linespeed is preferably from 1 to 500 m/minute, more preferably from 5 to300 m/minute, still more preferably from 10 to 100 m/minute, dependingon the time of curing of the adhesive. A too low line speed can lead topoor productivity or significant damage to the transparent protectivefilm so that it could be impossible to produce polarizing plates durableto an endurance test. A too high line speed can lead to insufficientcuring of the adhesive so that there is a possibility that the desiredadhesion can not be obtained.

A polarizing plate of the present invention may be used in practical useas an optical film laminated with other optical layers. Although thereis especially no limitation about the optical layers, one layer or twolayers or more of optical layers, which may be used for formation of aliquid crystal display etc., such as a reflector, a transflective plate,a retardation plate (a half wavelength plate and a quarter wavelengthplate included), and a viewing angle compensation film, may be used.Especially preferable polarizing plates are; a reflection typepolarizing plate or a transflective type polarizing plate in which areflector or a transflective reflector is further laminated onto apolarizing plate of the present invention; an elliptically polarizingplate or a circular polarizing plate in which a retardation plate isfurther laminated onto the polarizing plate; a wide viewing anglepolarizing plate in which a viewing angle compensation film is furtherlaminated onto the polarizing plate; or a polarizing plate in which abrightness enhancement film is further laminated onto the polarizingplate.

A reflective layer is prepared on a polarizing plate to give areflection type polarizing plate, and this type of plate is used for aliquid crystal display in which an incident light from a view side(display side) is reflected to give a display. This type of plate doesnot require built-in light sources, such as a backlight, but has anadvantage that a liquid crystal display may easily be made thinner. Areflection type polarizing plate may be formed using suitable methods,such as a method in which a reflective layer of metal etc. is, ifrequired, attached to one side of a polarizing plate through atransparent protective film etc.

As an example of a reflection type polarizing plate, a plate may bementioned on which, if required, a reflective layer is formed using amethod of attaching a foil and vapor deposition film of reflectivemetals, such as aluminum, to one side of a matte treated protectivefilm. Moreover, a different type of plate with a fine concavo-convexstructure on the surface obtained by mixing fine particle into theabove-mentioned protective film, on which a reflective layer ofconcavo-convex structure is prepared, may be mentioned. The reflectivelayer that has the above-mentioned fine concavo-convex structurediffuses incident light by random reflection to prevent directivity andglaring appearance, and has an advantage of controlling unevenness oflight and darkness etc. Moreover, the protective film containing thefine particle has an advantage that unevenness of light and darkness maybe controlled more effectively, as a result that an incident light andits reflected light that is transmitted through the film are diffused. Areflective layer with fine concavo-convex structure on the surfaceeffected by a surface fine concavo-convex structure of a protective filmmay be formed by a method of attaching a metal to the surface of atransparent protective film directly using, for example, suitablemethods of a vacuum evaporation method, such as a vacuum depositionmethod, an ion plating method, and a sputtering method, and a platingmethod etc.

Instead of a method in which a reflection plate is directly given to theprotective film of the above-mentioned polarizing plate, a reflectionplate may also be used as a reflective sheet constituted by preparing areflective layer on the suitable film for the transparent film. Inaddition, since a reflective layer is usually made of metal, it isdesirable that the reflective side is covered with a protective film ora polarizing plate etc. when used, from a viewpoint of preventingdeterioration in reflectance by oxidation, of maintaining an initialreflectance for a long period of time and of avoiding preparation of aprotective layer separately etc.

In addition, a transflective type polarizing plate may be obtained bypreparing the above-mentioned reflective layer as a transflective typereflective layer, such as a half-mirror etc. that reflects and transmitslight. A transflective type polarizing plate is usually prepared in thebackside of a liquid crystal cell and it may form a liquid crystaldisplay unit of a type in which a picture is displayed by an incidentlight reflected from a view side (display side) when used in acomparatively well-lighted atmosphere. And this unit displays a picture,in a comparatively dark atmosphere, using embedded type light sources,such as a back light built in backside of a transflective typepolarizing plate. That is, the transflective type polarizing plate isuseful to obtain of a liquid crystal display of the type that savesenergy of light sources, such as a back light, in a well-lightedatmosphere, and can be used with a built-in light source if needed in acomparatively dark atmosphere etc.

A description of the elliptically polarizing plate or circularlypolarizing plate in which the retardation plate is laminated to thepolarizing plate will be made in the following paragraph. Thesepolarizing plates change linearly polarized light into ellipticallypolarized light or circularly polarized light, elliptically polarizedlight or circularly polarized light into linearly polarized light orchange the polarization direction of linearly polarization by a functionof the retardation plate. As a retardation plate that changes circularlypolarized light into linearly polarized light or linearly polarizedlight into circularly polarized light, what is called a quarterwavelength plate (also called λ/4 plate) is used. Usually,half-wavelength plate (also called λ/2 plate) is used, when changing thepolarization direction of linearly polarized light.

Elliptically polarizing plate is effectively used to give a monochromedisplay without above-mentioned coloring by compensating (preventing)coloring (blue or yellow color) produced by birefringence of a liquidcrystal layer of a super twisted nematic (STN) type liquid crystaldisplay. Furthermore, a polarizing plate in which three-dimensionalrefractive index is controlled may also preferably compensate (prevent)coloring produced when a screen of a liquid crystal display is viewedfrom an oblique direction. Circularly polarizing plate is effectivelyused, for example, when adjusting a color tone of a picture of areflection type liquid crystal display that provides a colored picture,and it also has function of antireflection. For example, a retardationplate may be used that compensates coloring and viewing angle, etc.caused by birefringence of various wavelength plates or liquid crystallayers etc. Besides, optical characteristics, such as retardation, maybe controlled using laminated layer with two or more sorts ofretardation plates having suitable retardation value according to eachpurpose. As retardation plates, birefringence films formed by stretchingfilms comprising suitable polymers, such as polycarbonates, norbornenetype resins, polyvinyl alcohols, polystyrenes, poly methylmethacrylates, polypropylene; polyarylates and polyamides; aligned filmscomprising liquid crystal materials, such as liquid crystal polymer; andfilms on which an alignment layer of a liquid crystal material issupported may be mentioned. A retardation plate may be a retardationplate that has a proper retardation according to the purposes of use,such as various kinds of wavelength plates and plates aiming atcompensation of coloring by birefringence of a liquid crystal layer andof visual angle, etc., and may be a retardation plate in which two ormore sorts of retardation plates is laminated so that opticalproperties, such as retardation, may be controlled.

The above-mentioned elliptically polarizing plate and an above-mentionedreflected type elliptically polarizing plate are laminated platecombining suitably a polarizing plate or a reflection type polarizingplate with a retardation plate. This type of elliptically polarizingplate etc. may be manufactured by combining a polarizing plate(reflected type) and a retardation plate, and by laminating them one byone separately in the manufacture process of a liquid crystal display.On the other hand, the polarizing plate in which lamination wasbeforehand carried out and was obtained as an optical film, such as anelliptically polarizing plate, is excellent in a stable quality, aworkability in lamination etc., and has an advantage in improvedmanufacturing efficiency of a liquid crystal display.

A viewing angle compensation film is a film for extending viewing angleso that a picture may look comparatively clearly, even when it is viewedfrom an oblique direction not from vertical direction to a screen. Assuch a viewing angle compensation retardation plate, in addition, a filmhaving birefringence property that is processed by uniaxial stretchingor orthogonal biaxial stretching and a biaxial stretched film asinclined alignment film etc. may be used. As inclined alignment film,for example, a film obtained using a method in which a heat shrinkingfilm is adhered to a polymer film, and then the combined film is heatedand stretched or shrunk under a condition of being influenced by ashrinking force, or a film that is aligned in oblique direction may bementioned. The viewing angle compensation film is suitably combined forthe purpose of prevention of coloring caused by change of visible anglebased on retardation by liquid crystal cell etc. and of expansion ofviewing angle with good visibility.

Besides, a compensation plate in which an optical anisotropy layerconsisting of an alignment layer of liquid crystal polymer, especiallyconsisting of an inclined alignment layer of discotic liquid crystalpolymer is supported with triacetyl cellulose film may preferably beused from a viewpoint of attaining a wide viewing angle with goodvisibility.

The polarizing plate with which a polarizing plate and a brightnessenhancement film are adhered together is usually used being prepared ina backside of a liquid crystal cell. A brightness enhancement film showsa characteristic that reflects linearly polarized light with apredetermined polarization axis, or circularly polarized light with apredetermined direction, and that transmits other light, when naturallight by back lights of a liquid crystal display or by reflection from aback-side etc., comes in. The polarizing plate, which is obtained bylaminating a brightness enhancement film to a polarizing plate, thusdoes not transmit light without the predetermined polarization state andreflects it, while obtaining transmitted light with the predeterminedpolarization state by accepting a light from light sources, such as abacklight. This polarizing plate makes the light reflected by thebrightness enhancement film further reversed through the reflectivelayer prepared in the backside and forces the light re-enter into thebrightness enhancement film, and increases the quantity of thetransmitted light through the brightness enhancement film bytransmitting a part or all of the light as light with the predeterminedpolarization state. The polarizing plate simultaneously suppliespolarized light that is difficult to be absorbed in a polarizer, andincreases the quantity of the light usable for a liquid crystal picturedisplay etc., and as a result luminosity may be improved. That is, inthe case where the light enters through a polarizer from backside of aliquid crystal cell by the back light etc. without using a brightnessenhancement film, most of the light, with a polarization directiondifferent from the polarization axis of a polarizer, is absorbed by thepolarizer, and does not transmit through the polarizer. This means thatalthough influenced with the characteristics of the polarizer used,about 50 percent of light is absorbed by the polarizer, the quantity ofthe light usable for a liquid crystal picture display etc. decreases somuch, and a resulting picture displayed becomes dark. A brightnessenhancement film does not enter the light with the polarizing directionabsorbed by the polarizer into the polarizer but reflects the light onceby the brightness enhancement film, and further makes the light reversedthrough the reflective layer etc. prepared in the backside to re-enterthe light into the brightness enhancement film. By this above-mentionedrepeated operation, only when the polarization direction of the lightreflected and reversed between the both becomes to have the polarizationdirection which may pass a polarizer, the brightness enhancement filmtransmits the light to supply it to the polarizer. As a result, thelight from a backlight may be efficiently used for the display of thepicture of a liquid crystal display to obtain a bright screen.

A diffusion plate may also be prepared between brightness enhancementfilm and the above described reflective layer, etc. A polarized lightreflected by the brightness enhancement film goes to the above describedreflective layer etc., and the diffusion plate installed diffusespassing light uniformly and changes the light state into depolarizationat the same time. That is, the diffusion plate returns polarized lightto natural light state. Steps are repeated where light, in theunpolarized state, i.e., natural light state, reflects throughreflective layer and the like, and again goes into brightnessenhancement film through diffusion plate toward reflective layer and thelike. Diffusion plate that returns polarized light to the natural lightstate is installed between brightness enhancement film and the abovedescribed reflective layer, and the like, in this way, and thus auniform and bright screen may be provided while maintaining brightnessof display screen, and simultaneously controlling non-uniformity ofbrightness of the display screen. By preparing such diffusion plate, itis considered that number of repetition times of reflection of a firstincident light increases with sufficient degree to provide uniform andbright display screen conjointly with diffusion function of thediffusion plate.

The suitable films are used as the above-mentioned brightnessenhancement film. Namely, multilayer thin film of a dielectricsubstance; a laminated film that has the characteristics of transmittinga linearly polarized light with a predetermined polarizing axis, and ofreflecting other light, such as the multilayer laminated film of thethin film having a different refractive-index anisotropy; an alignedfilm of cholesteric liquid-crystal polymer; a film that has thecharacteristics of reflecting a circularly polarized light with eitherleft-handed or right-handed rotation and transmitting other light, suchas a film on which the aligned cholesteric liquid crystal layer issupported; etc. may be mentioned.

Therefore, in the brightness enhancement film of a type that transmits alinearly polarized light having the above-mentioned predeterminedpolarization axis, by arranging the polarization axis of the transmittedlight and entering the light into a polarizing plate as it is, theabsorption loss by the polarizing plate is controlled and the polarizedlight can be transmitted efficiently. On the other hand, in thebrightness enhancement film of a type that transmits a circularlypolarized light as a cholesteric liquid-crystal layer, the light may beentered into a polarizer as it is, but it is desirable to enter thelight into a polarizer after changing the circularly polarized light toa linearly polarized light through a retardation plate, taking controlan absorption loss into consideration. In addition, a circularlypolarized light is convertible into a linearly polarized light using aquarter wavelength plate as the retardation plate.

A retardation plate that works as a quarter wavelength plate in a widewavelength ranges, such as a visible-light band, is obtained by a methodin which a retardation layer working as a quarter wavelength plate to apale color light with a wavelength of 550 nm is laminated with aretardation layer having other retardation characteristics, such as aretardation layer working as a half-wavelength plate. Therefore, theretardation plate located between a polarizing plate and a brightnessenhancement film may consist of one or more retardation layers.

In addition, also in a cholesteric liquid-crystal layer, a layerreflecting a circularly polarized light in a wide wavelength ranges,such as a visible-light band, may be obtained by adopting aconfiguration structure in which two or more layers with differentreflective wavelength are laminated together. Thus a transmittedcircularly polarized light in a wide wavelength range may be obtainedusing this type of cholesteric liquid-crystal layer.

Moreover, the polarizing plate may consist of multi-layered film oflaminated layers of a polarizing plate and two of more of optical layersas the above-mentioned separated type polarizing plate. Therefore, apolarizing plate may be a reflection type elliptically polarizing plateor a semi-transmission type elliptically polarizing plate, etc. in whichthe above-mentioned reflection type polarizing plate or a transflectivetype polarizing plate is combined with above described retardation platerespectively.

Although an optical film with the above described optical layerlaminated to the polarizing plate may be formed by a method in whichlaminating is separately carried out sequentially in manufacturingprocess of a liquid crystal display etc., an optical film in a form ofbeing laminated beforehand has an outstanding advantage that it hasexcellent stability in quality and assembly workability, etc., and thusmanufacturing processes ability of a liquid crystal display etc. may beraised. Proper adhesion means, such as an adhesive layer, may be usedfor laminating. On the occasion of adhesion of the above describedpolarizing plate and other optical films, the optical axis may be set asa suitable configuration angle according to the target retardationcharacteristics etc.

In the polarizing plate mentioned above and the optical film in which atleast one layer of the polarizing plate is laminated, apressure-sensitive adhesive layer may also be prepared for adhesion withother members, such as a liquid crystal cell etc. As pressure-sensitiveadhesive that forms pressure-sensitive layer is not especially limited,and, for example, acrylic type polymers; silicone type polymers;polyesters, polyurethanes, polyamides, polyethers; fluorine type andrubber type polymers may be suitably selected as a base polymer.Especially, a pressure-sensitive adhesive such as acrylics typepressure-sensitive adhesives may be preferably used, which is excellentin optical transparency, showing adhesion characteristics with moderatewettability, cohesiveness and adhesive property and has outstandingweather resistance, heat resistance, etc.

Moreover, a pressure-sensitive adhesive layer with low moistureabsorption and excellent heat resistance is desirable. This is becausethose characteristics are required in order to prevent foaming andpeeling-off phenomena by moisture absorption, in order to preventdecrease in optical characteristics and curvature of a liquid crystalcell caused by thermal expansion difference etc. and in order tomanufacture a liquid crystal display excellent in durability with highquality.

The pressure-sensitive adhesive layer may contain additives, forexample, such as natural or synthetic resins, adhesive resins, glassfibers, glass beads, metal powder, fillers comprising other inorganicpowder etc., pigments, colorants and antioxidants. Moreover, it may be apressure-sensitive adhesive layer that contains fine particle and showsoptical diffusion nature.

Proper method may be carried out to attach a pressure-sensitive adhesivelayer to one side or both sides of the optical film. As an example,about 10 to about 40 weight % of the pressure-sensitive adhesivesolution in which a base polymer or its composition is dissolved ordispersed, for example, toluene or ethyl acetate or a mixed solvent ofthese two solvents is prepared. A method in which this solution isdirectly applied on a polarizing plate top or an optical film top usingsuitable developing methods, such as flow method and coating method, ora method in which a pressure-sensitive adhesive layer is once formed ona separator, as mentioned above, and is then transferred on a polarizingplate or an optical film may be mentioned.

A pressure-sensitive adhesive layer may also be prepared on one side orboth sides of a polarizing plate or an optical film as a layer in whichpressure-sensitive adhesives with different composition or differentkind etc. are laminated together. Moreover, when pressure-sensitiveadhesive layers are prepared on both sides, pressure-sensitive adhesivelayers that have different compositions, different kinds or thickness,etc. may also be used on front side and backside of a polarizing plateor an optical film. Thickness of a pressure-sensitive adhesive layer maybe suitably determined depending on a purpose of usage or adhesivestrength, etc., and generally is 1 to 40 μm, preferably 1 to 300 μm, andmore preferably 10 to 25 μm. If the thickness is less than 1 μm, itsdurability can be poor. If the thickness is more than 40 μm, separationor peeling is likely to occur due to foaming or the like so that theappearance can be degraded.

A temporary separator is attached to an exposed side of apressure-sensitive adhesive layer to prevent contamination etc., untilit is practically used. Thereby, it can be prevented that foreign mattercontacts pressure-sensitive adhesive layer in usual handling. As aseparator, without taking the above-mentioned thickness conditions intoconsideration, for example, suitable conventional sheet materials thatis coated, if necessary, with release agents, such as silicone type,long chain alkyl type, fluorine type release agents, and molybdenumsulfide may be used. As a suitable sheet material, plastics films,rubber sheets, papers, cloths, no woven fabrics, nets, foamed sheets andmetallic foils or laminated sheets thereof may be used.

In order to increase the adhesion between the polarizing plate and thepressure-sensitive adhesive layer, an anchor layer may be placed betweenthem.

An anchoring agent selected from polyurethane, polyester and a polymerhaving an amino group in its molecule may be preferably used as amaterial for forming the anchor layer. The polymer having an amino groupin its molecule is particularly preferred. The amino group in thepolymer molecule makes interaction such as a reaction or ionicinteraction with the carboxyl group or the like in thepressure-sensitive adhesive so that good adhesion can be ensured.

Examples of the polymers having an amino group in its molecule includepolymers of an amino group-containing monomer such as polyethyleneimine,polyallylamine, polyvinylamine, polyvinylpyridine, polyvinylpyrrolidine,and dimethylaminoethyl acrylate.

An antistatic agent may also be added to the anchor layer in order toimpart antistatic properties. Examples of the antistatic agent that maybe used to impart antistatic properties include ionic surfactants,electrically-conductive polymers such as polyaniline, polythiophene,polypyrrole, and polyquinoxaline, and metal oxides such as tin oxide,antimony oxide and indium oxide. Electrically-conductive polymers arepreferably used in view of optical properties, appearance, antistaticeffect, and stability of antistatic effect during heating orhumidifying. In particular, water-dispersible or water-solubleelectrically-conductive polymers such as polyaniline and polythiopheneare preferably used. When water-soluble or water-dispersibleelectrically-conductive polymers are used as a material for forming theantistatic layer, organic solvent-induced deterioration of the opticalfilm substrate can be prevented in the coating process.

In addition, in the present invention, ultraviolet absorbing propertymay be given to the above-mentioned each layer, such as a polarizer fora polarizing plate, a transparent protective film and an optical filmetc. and a pressure-sensitive adhesive layer, using a method of addingUV absorbents, such as salicylic acid ester type compounds, benzophenoltype compounds, benzotriazol type compounds, cyano acrylate typecompounds, and nickel complex salt type compounds.

A polarizing plate or an optical film of the present invention may bepreferably used for manufacturing various equipment, such as liquidcrystal display, etc. Assembling of a liquid crystal display may becarried out according to conventional methods. That is, a liquid crystaldisplay is generally manufactured by suitably assembling several partssuch as a liquid crystal cell, polarizing plates or optical films and,if necessity, lighting system, and by incorporating driving circuit. Inthe present invention, except that a polarizing plate or an optical filmby the present invention is used, there is especially no limitation touse any conventional methods. Also any liquid crystal cell of arbitrarytype, such as TN type, and STN type, π type may be used.

Suitable liquid crystal displays, such as liquid crystal display withwhich the above-mentioned polarizing plate or optical film has beenlocated at one side or both sides of the liquid crystal cell, and withwhich a backlight or a reflector is used for a lighting system may bemanufactured. In this case, the polarizing plate or optical film by thepresent invention may be installed in one side or both sides of theliquid crystal cell. When installing the polarizing plate or opticalfilms in both sides, they may be of the same type or of different type.Furthermore, in assembling a liquid crystal display, suitable parts,such as diffusion plate, anti-glare layer, antireflection film,protective plate, prism array, lens array sheet, optical diffusionplate, and backlight, may be installed in suitable position in one layeror two or more layers.

Subsequently, organic electro luminescence equipment (organic ELdisplay) will be explained. Generally, in organic EL display, atransparent electrode, an organic emitting layer and a metal electrodeare laminated on a transparent substrate in an order configuring anilluminant (organic electro luminescence illuminant). Here, an organicemitting layer is a laminated material of various organic thin films,and much compositions with various combination are known, for example, alaminated material of hole injection layer comprising triphenylaminederivatives etc., a luminescence layer comprising fluorescent organicsolids, such as anthracene; a laminated material of electronic injectionlayer comprising such a luminescence layer and perylene derivatives,etc.; laminated material of these hole injection layers, luminescencelayer, and electronic injection layer etc.

An organic EL display emits light based on a principle that positivehole and electron are injected into an organic emitting layer byimpressing voltage between a transparent electrode and a metalelectrode, the energy produced by recombination of these positive holesand electrons excites fluorescent substance, and subsequently light isemitted when excited fluorescent substance returns to ground state. Amechanism called recombination which takes place in a intermediateprocess is the same as a mechanism in common diodes, and, as isexpected, there is a strong non-linear relationship between electriccurrent and luminescence strength accompanied by rectification nature toapplied voltage.

In an organic EL display, in order to take out luminescence in anorganic emitting layer, at least one electrode must be transparent. Thetransparent electrode usually formed with transparent electricconductor, such as indium tin oxide (ITO), is used as an anode. On theother hand, in order to make electronic injection easier and to increaseluminescence efficiency, it is important that a substance with smallwork function is used for cathode, and metal electrodes, such as Mg—Agand Al—Li, are usually used.

In organic EL display of such a configuration, an organic emitting layeris formed by a very thin film about 10 nm in thickness. For this reason,light is transmitted nearly completely through organic emitting layer asthrough transparent electrode. Consequently, since the light thatenters, when light is not emitted, as incident light from a surface of atransparent substrate and is transmitted through a transparent electrodeand an organic emitting layer and then is reflected by a metalelectrode, appears in front surface side of the transparent substrateagain, a display side of the organic EL display looks like mirror ifviewed from outside.

In an organic EL display containing an organic electro luminescenceilluminant equipped with a transparent electrode on a surface side of anorganic emitting layer that emits light by impression of voltage, and atthe same time equipped with a metal electrode on a back side of organicemitting layer, a retardation plate may be installed between thesetransparent electrodes and a polarizing plate, while preparing thepolarizing plate on the surface side of the transparent electrode.

Since the retardation plate and the polarizing plate have functionpolarizing the light that has entered as incident light from outside andhas been reflected by the metal electrode, they have an effect of makingthe mirror surface of metal electrode not visible from outside by thepolarization action. If a retardation plate is configured with a quarterwavelength plate and the angle between the two polarization directionsof the polarizing plate and the retardation plate is adjusted to π/4,the mirror surface of the metal electrode may be completely covered.

This means that only linearly polarized light component of the externallight that enters as incident light into this organic EL display istransmitted with the work of polarizing plate. This linearly polarizedlight generally gives an elliptically polarized light by the retardationplate, and especially the retardation plate is a quarter wavelengthplate, and moreover when the angle between the two polarizationdirections of the polarizing plate and the retardation plate is adjustedto π/4, it gives a circularly polarized light.

This circularly polarized light is transmitted through the transparentsubstrate, the transparent electrode and the organic thin film, and isreflected by the metal electrode, and then is transmitted through theorganic thin film, the transparent electrode and the transparentsubstrate again, and is turned into a linearly polarized light againwith the retardation plate. And since this linearly polarized light liesat right angles to the polarization direction of the polarizing plate,it cannot be transmitted through the polarizing plate. As the result,mirror surface of the metal electrode may be completely covered.

EXAMPLES

Examples of the present invention are described below, but theembodiments of the present invention are not limited to these Examples.

<Glass Transition Temperature (Tg)>

The glass transition temperature was measured with a differentialscanning calorimeter (DSC) at a rate of temperature rise of 10°C./minute. A 5 mg sample was placed in a holding lidded vessel ofaluminum and crimped when used.

<Gel Fraction>

The adhesive for use in each example was coated to a release film withan applicator. After another release film was laminated on the coating,an electron beam was irradiated under the same conditions as in eachexample to cure the adhesive so that an adhesive layer was formed. Therelease films were separated from both sides of the adhesive layer, andabout 200 gm was sampled from the adhesive layer and measured for theweight (W1). The sample was then wrapped in a microporoustetrafluoroethylene film (film weight: W2) and tied with string. Thewrapped sample was immersed in about 50 ml of toluene for 4 days, andthen the soluble part was extracted. The sample was then dried in anoven at 110° C. for 1 hour, and the whole weight (W3) was measured. Thegel fraction (% by weight) of the pressure-sensitive adhesive layer wascalculated from the measurement values according to the followingformula: gel fraction (% by weight)=((W3−W2)/W1)×100

(Polarizer)

A 75 μm-thick polyvinyl alcohol film with an average polarization degreeof 2400 and a saponification degree of 99.9% by mole was immersed inwarm water at 30° C. for 60 seconds so that it was allowed to swell. Thefilm was then stretched to 3.5 times while it was dyed in a 0.3% byweight iodine solution (iodine:potassium iodide=0.5:8 in weight ratio)at 30° C. for 1 minute. The film was then stretched to a total stretchratio of 6 times, while it is immersed in an aqueous 4% by weight borateester solution at 65° C. for 0.5 minutes. After the stretching, the filmwas dried in an oven at 70° C. for 3 minutes to give a 26 μm-thickpolarizer. The polarizer had a moisture content of 13.5% by weight.

(Transparent Protective Film)

A lactonized polymethyl methacrylate film (LMMA, 20% in a lactonizationdegree, 30 μm in thickness, 0 nm in Re, 0 nm in Rth) was used as thetransparent protective film.

(Retardation)

The retardation was measured at a wavelength of 590 nm with aretardation meter (KOBRA21-ADH (product name) manufactured by OjiScientific Instruments) based on parallel Nicols rotation method. Thein-plane retardation Re, the retardation Rth in the thickness directionand Nz were calculated from nx, ny and nz values and the thickness (d)of the film, wherein nx is the refractive index in the direction of theslow axis of the film, ny is the refractive index in the direction ofthe fast axis of the film, nz is the refractive index in the directionof the thickness of the film, and d (nm) is the thickness of the film,and the direction of the slow axis is defined such that the in-planerefractive index of the film is the maximum in the direction of the slowaxis.

Example 1 Adhesive Curable Component

N-acryloylmorpholine was used as an adhesive.

(Preparation of Polarizing Plate)

The adhesive was applied to one side of the transparent protective filmwith a micro gravure coater (gravure roll: #180, rotational speed:140%/line speed) so that the transparent protective film was coated withthe adhesive coating with a thickness of 5 μm. The adhesive-coatedtransparent protective film was then laminated to both sides of thepolarizer with a roller machine. An electron beam was irradiated to theside of each of the bonded transparent protective films (both sides) sothat a polarizing plate including the polarizer and the transparentprotective films provided on both sides of the polarizer was obtained.The line speed was 20 m/minute, the accelerating voltage was 250 kV, andthe irradiation dose was 20 kGy. The adhesive layer had a Tg of 140° C.and a gel fraction of 72% by weight.

Examples 2 to 21 and Comparative Examples 1 to 11

Polarizing plates were obtained in the same manner as Example 1, exceptthat the type of the curable component, the mixing ratio of the curablecomponents and the thickness of the adhesive layer were changed as shownin Table 1. In Comparative Examples 4 to 6, 300 mJ of ultravioletirradiation was used in place of the electron beam irradiation. InComparative Examples 4 to 6, 3 parts by weight of a polymerizationinitiator was used and added to 100 parts by weight of the curablecomponent. The gravure roll was changed to a mirror surface type for anadhesive layer thickness of 0.1 μm, 0.3 μm or 0.5 μm, to a #300 type for0.8 μm or 1 μm, to #280 for 2 μm, to #250 for 3 μm, to #220 for 4 μm or4.2 μm, to #180 for 5 μm or 6 μm, and to #120 for 10 μm. The Tg and thegel fraction of the adhesive layer in each example are also shown inTable 1.

(Evaluations)

The polarizing plate obtained in each of Examples and ComparativeExamples was evaluated as described below. The results are shown inTable 1.

<Durability>

The resulting polarizing plate was cut into 15-inch diagonal pieces. Thecut pieces were placed in the crossed Nicols' configuration and attachedwith an acrylic pressure-sensitive adhesive to both sides of a 0.5mm-thick non-alkali glass member to form a sample. The sample was placedunder the following conditions:

(1) 200 cycles of a heat shock from −40 to 85° C. for 30 minutes; and

(2) 200 cycles of a heat shock from −30 to 70° C. for 30 minutes.

The time course of the state of the polarizing plate sample under eachcondition was evaluated according to the criteria below.

⊙: No cracking occurs.

◯: There are short cracks of 5 mm or less only at the end portion.

Δ: There are short linear cracks at the end portion and other portions,but the crack lines do not separate the polarizing plate into two ormore parts.

x: There are cracks at the end portion and other portions, and the cracklines separate the polarizing plate into two or more parts.

<Peel Strength>

The resulting polarizing plate was cut into a sample piece 15 mm×150 mmin size. The sample was attached to a glass plate with a double-sideadhesive tape (No. 500 manufactured by Nitto Denko Corporation). Astarting portion was formed between the transparent protective film andthe polarizer of the sample (polarizing plate). The starting portion waschucked by a variable-angle peel tester (manufactured by Asahi SeikoCo., Ltd.), and the peel strength (N/15 mm) was measured under theconditions of room temperature (23° C.), a peel angle of 90° and a peelspeed of 3000 mm/minute. Table 1 shows the average of the resultingmeasurement data between 50 mm and 100 mm.

TABLE 1 Curable Component (% by weight) Active Adhesive Layer DA-N-Substituted Amide Monomer Energy Tg Thickness Gel Fraction DurabilityPeel 141 HEAA N-MAN NIPAM ACMO Ray Type (° C.) (μm) (% by weight) (1)(2) Strength Example 1 — — — — 100  EB 140 5 72 ⊙ ⊙ 0.10 Example 2 — — —— 100  EB 140 1 72 ⊙ ⊙ 0.10 Example 3 — — — — 100  EB 140 0.1 72 ⊙ ⊙0.10 Example 4 12 — — — 88 EB 108 4.2 75 ◯ ⊙ 0.10 Example 5 12 — — — 88EB 108 2 75 ⊙ ⊙ 0.10 Example 6 12 — — — 88 EB 108 0.3 75 ⊙ ⊙ 0.10Example 7 25 — — — 75 EB 82 5 77 ◯ ⊙ 0.10 Example 8 25 — — — 75 EB 820.1 77 ⊙ ⊙ 0.10 Example 9 39 — — — 61 EB 69 1 71 ◯ ⊙ 0.12 Example 10 39— — — 61 EB 69 0.1 71 ⊙ ⊙ 0.12 Example 11 55 — — — 45 EB 62 2 75 ◯ ◯0.13 Example 12 55 — — — 45 EB 62 0.8 75 ◯ ⊙ 0.13 Example 13 55 — — — 45EB 62 0.1 75 ⊙ ⊙ 0.13 Example 14 — 100  — — — EB 98 5 75 ◯ ⊙ 0.24Example 15 — 100  — — — EB 98 0.5 75 ⊙ ⊙ 0.24 Example 16 — — 70 — 30 EB120 5 70 ⊙ ⊙ 0.20 Example 17 — — — 80 20 EB 134 5 70 ⊙ ⊙ 0.18 Example 18— 80 — — 20 EB 104 6 74 ◯ ⊙ 0.65 Example 19 — 80 — — 20 EB 104 1 74 ⊙ ⊙0.65 Example 20 — 60 — — 40 EB 117 4 73 ⊙ ⊙ 0.50 Example 21 — 40 — — 60EB 126 5 72 ⊙ ⊙ 0.15 Comparative 100  — — — — EB 20 3 82 X X 0.80Example 1 Comparatlve 100  — — — — EB 20 1 82 X Δ 0.80 Example 2Comparative 100  — — — — EB 20 0.1 82 X Δ 0.80 Example 3 Comparative 50— — — 50 UV 50 1 20 Δ ◯ 0.50 Example 4 Comparative 50 — — — 50 UV 50 520 Δ Δ 0.50 Example 5 Comparative 50 — — — 50 UV 50 10 20 X X 0.50Example 6 Comparative 70 — — — 30 EB 45 0.1 78 Δ ◯ 0.60 Example 7Comparative 70 — — — 30 EB 45 5 78 Δ ◯ 0.60 Example 8 Comparative 70 — —— 30 EB 45 10 78 X X 0.60 Example 9 Comparative 25 — — — 75 EB 82 10 77X ◯ 1.00 Example 10 Comparative 39 — — — 61 EB 69 10 71 X Δ 1.50 Example11

In Table 1, ACMO represents N-acryloylmorpholine, DA-141;2-hydroxy-3-phenoxypropyl acrylate (DA-141 manufactured by NagaseChemteX Corporation), HEAA; N-hydroxyethylacrylamide, N-MAN;N-methylolacrylamide, NIPAM; N-isopropylacrylamide, EB; electron beam,and UV; ultraviolet ray.

What is claimed is:
 1. A polarizing plate, comprising a polarizer; anadhesive layer; and a transparent protective film bonded to at least oneside of the polarizer with the adhesive layer interposed therebetween,wherein the adhesive layer is formed from an active energy ray curingadhesive containing at least one curable component comprising a compoundhaving a (meth)acryloyl group, wherein the compound having a(meth)acryloyl group contains N-hydroxyethylacrylamide andN-acryloylmorpholine, and the adhesive layer has a glass transitiontemperature (Tg) of 60° C. or more, and a thickness of 0.01 μm to 5 μm.2. The polarizing plate according to claim 1, wherein the Tg (° C.) ofthe adhesive layer represented by A and the thickness (μm) of theadhesive layer represented by B satisfy the mathematical formula (I):A−12×B>58.
 3. The polarizing plate according to claim 1, wherein theadhesive layer has a gel fraction of 50% by weight or more.
 4. Thepolarizing plate according to claim 1, wherein a content ofN-hydroxyethylacrylamide is 40% by weight or more based on the totalamount of N-hydroxyethylacrylamide and N-acryloylmorpholine.
 5. Thepolarizing plate according to claim 1, wherein the curable componentfurther contains a monofunctional (meth)acrylate having an aromatic ringand a hydroxy group.
 6. The polarizing plate according to claim 1,wherein the active energy ray curing adhesive is an electron beam curingadhesive.
 7. The polarizing plate according to claim 1, wherein thetransparent protective film is made of one selected from the groupconsisting of a cellulose resin, a polycarbonate resin, a cyclic olefinpolymer resin and a (meth)acrylic resin.
 8. An optical film in which atleast one layer of the polarizing plate according to claim 1 islaminated.
 9. An image display, comprising the polarizing plateaccording to claim
 1. 10. An image display, comprising the optical filmaccording to claim 8.